A positioning apparatus receives electric waves sent from satellites by using an SPS receiver, and removes carriers from the electric waves so as to acquire SPS received signals. A correlator then carries out a correlation calculation by using the pseudo pattern codes of the satellites and the SPS received signals.
A data processing unit of the positioning apparatus selects the largest correlation value from correlation values outputted from the correlator, and calculates a pseudo distance between each of the satellites and the SPS receiver on the basis of a position shown by the largest one of the correlation values to determine the current position (refer to, for example, patent reference 1).
[Patent reference 1] U.S. Pat. No. 6,289,041 B1
Because the prior art positioning apparatus is constructed as mentioned above, under an environment in which the powers of the electric waves which come directly from the satellites are strong while the powers of multi-pass electric waves which come indirectly from the satellites and the noise level are weak, the current position can be determined with a high degree of precision. However, in a case in which the prior art positioning apparatus carries out positioning when it is placed the valley between buildings or indoor of a building, such a building serves as an obstruction and the powers of the electric waves which come directly from the satellites become weaker, and therefore a correlation value associated with multi-pass electric waves and extraneous noises may be maximized among the correlation values outputted by the correlator. In such a case, because the current position is determined on the basis of not the electric waves that come directly from the satellites, but the multi-pass electric waves and extraneous noises, there is a problem that the prior art positioning apparatus cannot determine the current position correctly.
The present invention is made in order to solve the above-mentioned problem, and it is therefore an object of the present invention to provide a positioning apparatus which can determine the current position correctly even under a receiving environment in which the electric waves which come directly from the satellites become weak.